Drum centrifuge with rotating worm conveyor



J. s. BYE-JQRGENSEN Erm.

DRUM CENTRIFUGE WITH ROTATING WORM CONVEYOR[/////////////////////////////{y//II United States Patent O U.S. Cl.233--7 4 Claims ABSTRACT F THE DISCLOSURE This invention relates to adrum centrifuge for wastewater-sludge comprising a drum having twosections therein. Worm conveyor means mounted for free relativerotatable movement in one of said drum sections conveys moist solidswhich have been separated from the liquid. The other drum section has anoblique guiding surface along which the separated solids are guided andpassed to the worm conveyor means. The worm conveyor means are disposedentirely within said one section and said other section is substantiallyfree of obstructions to provide free axial and radial movement of thesolids and liquids therethrough.

The present invention relates to a drum centrifuge, particularly forwastewater sludge, comprising a rotating confveyor worm for scraping outsolids separated in the interior of the centrifuge; at least one feedconduit for the suspension to be separated, said feed conduit debouchingin a part of the centrifuge provided in its interior with oblique,preferably substantially conical guiding surfaces, to which part of thecentrifuge the conveyor worm does not extend; an exit opening for theseparated solids; and at least one discharge for liquid totally orpartly puried from solids.

Drum centrifuges are known in which a worm conveyor is placed inside thedrum and rotate during operation at a speed differing from the speed ofrotation of the drum itself. In other words, the worm conveyor has arotation relative to the drum, and thereby the worm conveyor conveys thesolids separated on the inner wall of the drum onto a discharge openingor place. A known drum centrifuge of this type is adapted so as tointroduce the sludge-containing suspension at a point between the endsof the space in the drum, whereas the separated solids are discharged inone end and the centrifuged and thereby partly purified liquid isdischarged in the other end 0f the drum. By this arrangement the twocomponents to be separated, solids and liquid, move in mutualcountercurrent and this counter-movement gives rise to so high aturbulence that the separation becomes unsatisfactory, because solidswill have a tendency to return from the conveyor worm to the liquid. Inuse for instance for centrifuging wastewater sludge from biologicalwater purification plants, the centrifuged liquid after suchcountercurrent conveying may still contain about 50% of solids,frequently in so iinely emulsified or dispersed form that a removal ofsaid solids in a subsequent centrifugation step will cause difficulties.

It has been proposed to alter the described known drum centrifuge insuch a manner that the feed conduit for the sludgecontaining suspensiondebouches in one end of the drum and the exit opening for the solids inthe opposite end of the drum, whereas outlets for the discharge ofpurified liquid are situated in a zone between the ends of the drum.Hereby the sludge-containing suspension introduced in the centrifugedrum will be flowing in the same direction as the separated solids,which results in a considerably reduced turbulence and hence improvedseparation. By a drum centrifuge thus adapted, it is possible to achieverather satisfactory separation, even of difiicultly separablesuspensions such as organic sludge-containing liquids from biologicalwastewater-purification plants. i

In the above-mentioned known centrifutges containing worm-conveyors itis known to have the drum and the worm conveyor frusto-conical orsubstantially frusto-conical at least over part of their length. In suchcases the exit opening for the solids is situated in the narrow end ofthe truncated cone and in a zone within the cylindrical surface of theliquid formed during operation of the centrifuge. It is hereby possiblewithout diiiiculty to remove the solids in a condition freed from waterto a considerable degree; for instance when the centrifuge is used fortreating sludge from biological water-purification, it is possible toremove the solids from the centrifuge in a condition so that the solidscan be shoveled and placed in heaps having a slope of for instance Inthe known drum centrifuges of this type the worm conveyor is situated atthe inner wall of the drum along the full or approximately full lengthof the latter.

It has now been found that it is possible to achieve a still betterseparation effect or centrifugation-effect than is possible by theapparatuses discussed hereinbefore. This is possible if a drumcentrifuge of the above-described main type is so constructed that theinlet for sludge-containing suspension and the discharge or outlet forwater are placed in a part of the centrifuge drum where there is no wormconveyor, or rather to which the worm conveyor does not extend, and iffurthermore this part of the centrifuge is provided with oblique,preferably substantially conical (frusto-conical) guiding surfaces alongwhich the separated solids are led to the worm conveyor under theinfluence of the centrifugal forces. From the specification to the U.S.Pat. No. 3,322,336 a centrifuge is known constructed according to thisprinciple, but in contradistinction to the above-mentioned centrifuges,it is not able to give a substantially turbulence-free treatment of thesludge-containing liquid, especially wastewatersludge, in the said partof the centrifuge to which the conveyor worm does not extend. This isdue to the fact that the centrifuge described in the said U.S. Patentspeciiication No. 3,322,336 in the said part 4'of the centrifuge isprovided with a number of axial and radial partitions so as to subdividethe centrifuge part in question into several separating chambers. Theradial partitions of these chambers by narrow slots or annular gaps,serving as discharges, are in distance from the inner surface of thedrum wall and furthermore there are small openings in the partitions soas to allow liquid to pass. The openings and annular gaps or slotsduring the operation of the centrifuge cause turbulence in thesludge-containing liquid in the said part of the drum which issubdivided into said chambers. The partitions will hamper the movementof water and sludge in the direction of movement, especially axiallyrelative to the longitudinal axis of the drum, and the part of the drumcontaining the conveyor worm is preferably substantially frusto-conical,the exit opening for the solids being situated in the narrow end of thetruncated cone. If this is the case, the centrifuge drum may expedientlyhave such a shape that the inner guiding surfaces, along which thesolids slide onto the intake end of the conveyor worm are constituted bythe inner side of the wall of a substantially frusto-conical part of thedrum, the largest base-perimeter of the last mentioned truncated conebeing joined to the largest base-perimeter of the first mentioned drumpart, i.e. the one containing the conveyor, the spaces in the two partsof the drum being in open connection with each other in the axialdirection. Thereby the drum substantially has the shape of a doubletruncated cone with the greatest thickness near the middle. Thesludge-containing suspension is fed into the end of the drum into whichthe conveyor does not extend, and the inlet in fact debouches quite nearthe narrow end of that part of the drum. The solids are discharged inthe opposite narrow end of the drum.

In a more preferred embodiment of the drum centrifuge according to theinvention, the part of the drum containing the worm conveyor is alsosubstantially frustoconical with the exit for the solids in the narrowend of this drum part. In this more preferred embodiment, however, theoblique guiding surfaces, along which the solids are led to the wormconveyor, are consituted by a substantially frusto-conical ldrum spaceor chamber the largest base-perimeter of which is situated near theinner end of the widest end of the worm conveyor, whereas the smallestbase-perimeter of the said space is situated in a plane between the endplanes of the worm conveyor. In this preferred case the two truncated orapproximately truncated cones are uni-directional, i.e. have theirnarrowest end turned in the same direction. In its entirety the drum inthis case has substantially the outer shape of a single truncated cone.This embodiment has the particular advantage that it may be constructedwith smaller length compared to the capacity of the aforementionedembodiment, because of the total length of the drum will be little morethan the length of the worm conveyor. The shorter length of the druminvolves a shorter distance between the bearings, which may be ofimportance in large centrifuges and at the very high rotation-velocitieswhich may come into question.

The discharge or discharges for liquid preferably start from an area inthe centrifuge being situated near the circle of intersection betweenthe cylindrical surface of the liquid during operation, and the largestbase of the conical guiding surfaces. Hereby it is obtained that thepurified liquid is discharged from an area in the centrifuge which is asdistant as possible from the area in which the actual separation takesplace, and this ensures the best possible purity of the dischargedliquid.

A feed line for chemicals with which to treat the suspension may debouchin the centrifuge near the debouching of the feed line forsludge-containing suspension. In some cases it may be desirable to treatfor instance wastewater sludge with various substances in order to causevarious chemical reactions, and in the manner stated there is obtainedthe possibility of dosing the addition of the chemicals in a very variedmanner; furthermore, the chemicals will come into contact with thesuspension at once upon its introduction.

The drum centrifuge according to the invention will be described more indetail with reference to the drawing. In the drawing, FIGS. 1 and 2schematically show longitudinal sections of two different embodiments ofthe drum centrifuge according to the invention.

In FIG. 1 a double frusto-conical dum 11 is fixedly mounted on a shaft12 which in a manner not shown is rotatably mounted in bearings 13 onsupports 14. The shaft 12 is driven in conventional manner, for instanceby the aid of V-belts and a pulley 15. In one end the shaft 12 isenclosed in a coaxial tubular shaft 16, rotatably mounted on the shaft12 by the aid of bearing .17 (not shown in detail). The shaft 16 isadapted to rotate with a velocity differing from that of the shaft 12and may for instance be driven by V-belts and a pulley 18. It ispossible to drive the two shafts from one source of power, suitabletransmissions ensuring the speed of rotation of the two shafts beingdifferent.

In a suitable manner, for instance as in the embodiment shown, i.e. bythe aid of spokes 19, the shaft 16 supports a Worm conveyor 20 adaptedto convey solids onto an exit opening 21 in the one end of the drum. Asthe worm conveyor 20 is fxedly connected to the shaft 16, and as thedrum 11 by the aid of the spokes 22 or in another suitable manner isfixedly connected to the 4 shaft 12, and as these two shafts rotate atdifferent velocities, the worm conveyor 20 in operation will rotaterelative to the drum 11, and this relative rotation causes the transportof the solids by the conveyor.

The worm conveyor does not extend along the entire length of the drum11, but only along one conical part thereof, as in FIG. 1, the leftfrusto-conical end 23 of drum 11. The right-hand end 24 of drum 11 islikewise frusto-conical and the two frusto-cones are joined at thelargest, common base perimeter. Frusto-conical part 24 of drum 11accordingly is not provided with the conveyor work, but its inner wallconstitutes a fnlsto-conical guiding surface for sludge-containingliquid suspension introduced into the drum in order to be separated bythe centrifugal effect.

In the embodiment shown in FIG. 1, the suspension is introduced via aconduit 25 and a channel 26 in the shaft 12. This channel 26 debouchesin the drum space through one or more openings 27 situated adjacent tothe narrowest end of drum part 24. By the aid of suitable members (notshown) the conduit 25 is watertightly connected with the channel 26 inshaft .12 in a manner so as not to disturb the rotation. Near the widestplane of the drum 11 there is a number (for instance six) of orifices 28for pipes 29 which extend through the wall of drum 11 and debouch into adischarge channel 30 for purified liquid; this discharge channel may forinstance be limited by a cover 31 slidably connected to the drum 11 atthe widest part of the latter.

In the shaft there may be provided, but need not be provided, a furtherchannel 32 to be fed for instance with substances for treatment of thesludge. Channel 32 may be fed from conduit 33 and debouches in the drumspace via one or more openings 34 adjacent to open ings 27.

Adjacent to the exit opening 21 there is a suitable discharge channel 35through which the separated solids are discharged.

The drum centrifuge thus described functions in the following manner.When the suspension is supplied via conduit 25, channel 26 and openings26, it flows into the space of the drum 11 in its right-handfrusto-conical part 24, wherein no part of the worm conveyor is present.The rotation of the drum will cause separation of liquid and solids, andthis separation will take place only in the part 24 of the drum. Solelyunder the influence of the centrifugal force, the solids will slidealong the inner conical wall of the drum part 24, this Wall acting as aguiding surface and conducting the solids onto the commencing end orintake end of the worm conveyor 20, situated near the widest part ofdrum 11. Worm conveyor 20 is also kept in rotation and at such a speedthat it has a rotation relative to the drum, the direction of therelative rotation being so as to conduct the solids towards exit opening2.1. Through this opening the solids leave the drum and are dischargedvia channel 35 from which they can be removed. Like the dischargechannel 30, the channel 35 may pass a base plate (not shown) on whichsupports 14 are mounted.

During operation of the centrifuge, the surface of liquid adjusts itselfalong a cylindrical level or surface intimated in the drawing by brokenlines 37. Adjacent to this surface, between it and the wall of the drum,the orifices 28 are situated. Through these orifices the water purifiedfrom solids enters pipes 29 and passes to the discharge channel 30. Thepipes 29 may be led through a further channel in shaft 32. The orifices28, however, should preferably be situated as shown in FIG. 1, i.e.close to the largest base of the truncated cone formed by drum part 24,because hereby the place where the liquid actually leaves the drum spaceis farthest possible from the place at which the suspension to beseparated enters the drum space.

The level surface 3'7 has a longer distance from the drum and Wormconveyor axes than the periphery of the solids exit opening 21, and forthat reason the solids leaving that opening have to a considerabledegree been freed from liquid.

Simultaneously with the introduction of suspension from conduit 25, itis possible, if desired, to add liquid treatment substances from conduit33 via channel 32 and openings 34. Such a liquid for addition to thesuspension will thereby at once be intermixed with the suspensionentering the drum space via openings 27, a good intermixing beingthereby ensured.

The spokes 22 support the drum 23, 24 in such a man ner that the drumpart 23 forms a projecting end. The spokes 22 may be replaced by abearing inside the channel 35 and adapted in such a manner that thesludge from opening 21 can pass around such bearing, for instancethrough suitable opening in the prolonged drum part 23.

Since there are no substantial turbulence-creating hindrances to thefree movement of the liquid in the drum part 24 containing no part ofthe worm conveyor, the centrifugation operation will essentially be freefrom turbulence and hence ensure an effective separation of liquid andsolids.

The particularly preferred embodiment of the drum centrifuge shown inFIG. 2 comprises a substantially frusto-conical drum 41 iixedly mountedon a shaft 44 rotatably mounted on bearings 13 on supports 14. Themounting of drum 41 on shaft 44 may for instance be carried out by theaid of an end plate 43. In FIG. 2, end plate 43 is shown as a flatplate, but need not be flat. It may for instance be arched or conical(concave or preferably convex), or may otherwise deviate from the flatform. The end plate 43 is preferably convex, domeshaped.

Thc drum 41 is driven in a suitable manner, for instance -by the aid ofbelts and al pulley 15. In one end the shaft 44 is enclosed in a coaxialhollow shaft 45 which is rotatable relative to the shaft 44 in the samemanner as shaft 16 (FIG. l) relative to shaft 12; shaft 45 may forinstance be driven by belts over a pulley 18, and on shaft 45 is mounteda worm conveyor 46 by the aid of spokes 42. The worm conveyor is adaptedto and driven in such a manner relative to the drum 41, that conveyor 46transports solids centrifuged olf from the suspension in the directionfrom the widest to the narrowest end of said conveyor. At the narrowestend of the conveyor, the solids leave it and are discharged via the exitopening 21 and a discharge channel 35 in the same manner as theembodiment shown in FIG. I.

The worm conveyor 46 extends along substantially the entire length ofthe inner conical wall of drum 41. On the shaft 44 is mounted asubstantially frusto-conical guiding means 47, made for instance ofsteel or some other metal. The orientation of guiding means 47 is thesame as the orientation of the frusto-conical drum 41, i.e. thenarrowest end of both is turned in the same direction; the narrowest endof the guiding means 47 is situated in a plane between the widest end ofthe very same guiding means 47 and the narrowest end of the drum. Thelarg est perimeter of the frusto-conical guiding means 47 is situatednear the inner edge of the widest end of the conveyor Worm 46. Guidingmeans 47 together with end plate 43 define a substantially conical partor compartment 48 in the drum, and in this compartment the actualseparation takes place. If end plate 43 is not at, the base of thetruncated cone constituting said compartment will not be flat, but thishas no influence on the principle of the compartment 48, which is thatthe inner (right-hand in FIG. 2) side of guiding means 47 serves assubstantially conical guiding surface along which the solids slide tothe intake end of the worm conveyor under the iniiuence of thecentrifugal forces.

In the shaft 44 there is a channel 49 in connection with a feed conduit50 for sludge-containing liquid or suspension to be separated in thedrum centrifuge. The channel 49 debouches in compartment 48 by openings51 situated adjacent to the narrowest end of guiding means 47. Guidingmeans 47 as mentioned act as guiding surface along which the solidsseparated from the suspension are led to the beginning end of wormconveyor 46. The embodiment accordingto FIG. 2 may also have a furtherchannel 32 in shaft 44 and in connection with a supply conduit 33 for atreatment liquid such as chemicals with which to treat the suspension;such channel 32, if present, debouches in compartment 48 via openings 34in the neighborhood of openings '51.

In end plate 43 there is a suitable number of holes or small pipes 5,2through which liquid totally or partly purified from solids may leavethe drum 41, to wit leave the drum from drum compartment 58. Via theseholes or pipes the purified liquid enters a discharge channel 54 forpurified liquid; this channel 54 may for instance be delimited by ascreen 53.

The embodiment shown in FIG. 2 is shorter than that shown in FIG. l withregard to capacity, but essentially it functions in the same manner.When the suspension flows into the drum 46 via openings 51 and the drumrotates, a separation will be caused. Under the influence of thecentrifugal forces, solids centrifuged off slide along the inner wall ofguiding means 47 delimiting the compartment 48, and thereby the solidsarrive to the largest perimeter of said guiding means. Here the solidsare caught rby the worm conveyor 46 and conveyed onto the exit opening21. The liquid level or surface adjusts itself as a cylindrical surface37, and adjacent to this surface, yet between it and the outer wall ormantle of the drum, the openings or pipes 52 are situated; the purifiedliquid leaves the drum via these. In the embodiment according to FIG. 2,as well as in that according to FIG. 1, the actual spot of liquiddischarge, i.e. the openings or pipes 52, are situated as far aspossible from the area where the actual separation occurs and therebyone ensures the greatest possible purity of the discharged liquid; nocountercurrents will be formed and no turbulence created.

The suspension introduced in the drum will in none of the embodimentscome into flowing contact with the solids centrifuged off and thereafterbeing present in the turns of the worm conveyor; consequently thesuspension cannot give rise to turbulence which would whirl up thesolids and subdivide them. There furthermore are no hindrances to theflow in the compartment 48 and therefore no turbulence can be createdthere. The separation of solids and liquid accordingly becomes veryefiicient.

In the present specication and appended claims, by the expressionsoblique guiding surface, substantially conical or substantiallyfrusto-conical and similar expressions, we mean rotational-symmetricalsurfaces the generatrix of which is inclined or oblique to the axis,i.e. one end of the generatrix has a larger radial distance from theaxis than the other end of the generatrix. From the radially nearest tothe radially farthest end, the generatrix consistently is gaining largerdistance from the axis but it need not be a smooth or continuous curve;the generatrix may have angles or bends. The generatrix may be astraight line, in which case the guiding surface is a true truncatedcone. The generatrix may also be more or less curved, possibly sinuous,and convex or concave.

We claim:

1. A drum centrifuge for wastewater-sludge, comprising a drum having twosections therein, worm conveyor means mounted for relative rotatablemovement within one of said drum sections to convey moist solids whichhave been separated from the liquid, said other drum section having anoblique guiding surface along which separated solids are disposed andguided by the action of centrifugal force, said guiding surface havingits larger end disposed adjacent the inlet of the worm conveyor meanswhereby separated solids are passed from said guiding surface to saidworm conveyor means inlet, feed inlet means conducting Wastewater-sludgeinto said other drum section, and puried water discharge means leadingfrom said other drum section, said worm conveyor means being disposedentirely within said one drum section, said other section beingconstructed and arranged to provide an undivided and uncompartmentalizedspace substantially free of obstructions to facilitate free axial andradial movement of the solids and liquids therethrough, thereby toreduce turbulence to a minimum.

2. A drum centrifuge according to claim 1 wherein said one drum sectionand said worm conveyor means each have a substantially conicalconfiguration, said worm conveyor means having a discharge at thesmaller end of said one drum section, said oblique guiding surface beingformed by the inner wall of a substantially truncated conicalcompartment, the largest end of which is disposed adjacent the largestend of said one drum section.

3. A drum centrifuge according to claim 2 wherein said adjacent largerends of said one and said other compartments are disposed between thesmaller ends of said one and said other compartments considered along alongitudinal axis.

4. A drum centrifuge according to claim 3 wherein said smaller end ofsaid other Icompartment is disposed between the smaller and larger endsof said one compartment considered along a longitudinal axis.

References Cited UNITED STATES PATENTS 2,795,635 6/1957 McBride 233-73,322,336 5/1967 LOhse 233-7 FOREIGN PATENTS 16,5 32 Germany. 1,021,29712/1957 Germany.

ROBERT W. JENKINS, Primary Examiner

